tgafb: remove a redundant non-mono test in mono imageblit

There is a test in tgafb_mono_imageblit() for a colour image with a fall-back
to cfb_imageblit().  The test is not necessary as the only caller, which is
tgafb_imageblit(), checks it too and only invokes this function for monochrome
images.  It looks like a left-over from before some changes to
tgafb_imageblit().

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Cc: Antonino Daplas <adaplas@pol.net>
Cc: Jay Estabrook <Jay.Estabrook@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>